Fuel cells are used as an electrical power source in many applications. In particular, fuel cells are proposed for use in automobiles to replace internal combustion engines. A commonly used fuel cell design uses a solid polymer electrolyte (“SPE”) membrane or proton exchange membrane (“PEM”), to provide ion transport between the anode and cathode.
In proton exchange membrane type fuel cells, hydrogen is supplied to the anode as fuel, and oxygen is supplied to the cathode as the oxidant. The oxygen can either be in pure form (O2) or air (a mixture of O2 and N2). PEM fuel cells typically have a membrane electrode assembly (“MEA”) in which a solid polymer membrane (i.e., ion conducting membrane) has an anode catalyst on one face, and a cathode catalyst on the opposite face. The anode and cathode layers of a typical PEM fuel cell are formed of porous conductive materials, such as woven graphite, graphitized sheets, or carbon paper to enable the fuel to disperse over the surface of the membrane facing the fuel supply electrode. Each electrode has finely divided catalyst particles (for example, platinum particles) supported on carbon particles to promote oxidation of hydrogen at the anode, and reduction of oxygen at the cathode. Protons flow from the anode through the ionically conductive polymer membrane to the cathode where they combine with oxygen to form water, which is discharged from the cell. The MEA is sandwiched between a pair of porous gas diffusion layers (“GDL”) which in turn are sandwiched between a pair of non-porous, electrically conductive elements or plates. The plates function as current collectors for the anode and the cathode, and contain appropriate channels and openings formed therein for distributing the fuel cell's gaseous reactants over the surface of respective anode and cathode catalysts. In order to produce electricity efficiently, the polymer electrolyte membrane of a PEM fuel cell must be thin, chemically stable, proton transmissive, non-electrically conductive and gas impermeable. In typical applications, fuel cells are provided in arrays of many individual fuel cell stacks in order to provide high levels of electrical power.
Some prior art fuel cells include sub-gaskets between the catalyst electrodes and ion conducting membrane. During manufacture and operation of a fuel cell, it is possible that one or more catalyst containing particles can become attached to the sub-gasket, and these unintended particles are capable of generating levels of thermal energy that have the ability to elevate temperatures of polymer based sub-gasket material to their melt temperatures when exposed to combustible mixtures of hydrogen and oxygen. The fuel cell stack is regularly exposed to such combustible mixtures as a method to start the fuel cell from freeze conditions or during anode bleed to the cathode to purge nitrogen. In many cases, the sub-gasket material becomes the primary thermal conduction media for the energy generated. Although the prior art subgasket designs work reasonably well during normal operation, these particles represent a manufacturing defect that can overwhelm the thermal properties of these sub-gaskets.
Accordingly, the present invention provides improved designs for dissipating the thermal energy generated by unintended particles resulting in localized heating in a fuel cell.